Many manufacturing processes, such as mining and minerals, cement, bulk powder, or grains and cereal production and processing, require equipment that is capable of conveying, blending, mixing, or metering solids with varying degrees of abrasive qualities. In some cases, such as in cement or mineral production, the solids can be powdered and highly abrasive. For a variety of reasons it is often necessary to quickly open or close a pipe or duct conveying such solid materials. One valve type that is well-suited to the control of such dry material processes is a flap dust valve, for example as shown in U.S. Pat. No. 5,241,989. While this type of valve can provide excellent service in such abrasive environments, it is sometimes not well-suited for use in space-limited installations. Often, gate valves must be turned to when a lower-profile valve is required.
When higher closure forces are desired, gate valves employing wedge-shaped gates, such as disclosed in U.S. Pat. No. 3,179,372, may be used. In this type of valve, the valve gate is formed in a wedge shape and the valve seat is angled on both the upstream and downstream sides of the valve to conform to the wedge-shaped gate. The wedging action created between the gate and opposed valve seats allows for higher closing forces at relatively lower gate actuation force.
While gate valves can be ideal in liquid systems, in dry materials systems, especially those involving abrasive materials, gate valves can present certain drawbacks. In particular, gate valves generally rely on a uniform leading edge to create a seal against the valve seat. However, in abrasive, dry materials systems, the gate leading edge can be subject to significant erosion as the valve gate opens and closes, which effect can be exacerbated due to increased velocity of particles when the valve is in a partly opened state before fully opening or fully closing. Once the leading edge of the gate is eroded, it can be impossible to achieve a tight seal, and leaks from an initial loss of seal only accelerate the erosion of the valve seat and sealing edge of the gate. Wedge-shaped gate valves present an additional drawback in that the downstream valve seat is directly impinged upon by the flow of dust or abrasive particles, leading to greater erosion on the downstream valve seat than the upstream valve seat. If the opposed valve seats do not remain symmetrical, the wedging action of the gate may be compromised resulting in less than a complete seal. Again, once a seal is initially compromised in an abrasive environment, it quickly deteriorates. There is thus a need for a gate-type valve with improved sealing and wear-resistance characteristics for use in dry materials processes.